Patent GB-719883-A (GB)
Title: Improvements in or relating to telecommunication systems
Inventor: MURRAY LAWRENCE JOHN
IPC: H04Q3/00
Filed: 1952-06-27
Abstract: 719,883. Automatic exchange systems. AUTOMATIC TELEPHONE & ELECTRIC CO., Ltd. June 11, 1953, [June 27, 1952.] No. 16185/52. Class 40 (4). In a switching arrangement for connecting one of a number of inlets, which are multipled over the corresponding contacts of a group of bridges of a crossbar switch, to an available one of a larger number of outlets, which are connected to individual contacts of a second group of bridges of the same switch, the bridges of the two groups being connected together by links, means are provided which, on an available outlet being found .by test means, serve to operate a select and a bridge magnet to connect the available outlet through the appropriate bridge of the second group to the associated bridge of the first group, and to operate a select and a bridge magnet to connect the one outlet to the said bridge of the first group. General discription.-The system described is designed to utilise, as switches in the talking circuit, the 12 x 10 crossbar switch, which with double-group working will serve 200 outlets. The trunking diagram of Fig. 1 may be employed for an exchange with up to 10,000 subscribers and 15 groups of junctions. Only two selection stages are used, viz. line finder/final selector and group selector stages. For exchanges with. more subscribers and a large volume of junction traffic an extra group selection stage would be required. The uniselector symbol represents one bridge of a crossbar switch, of which the wiper symbol represents the bridge common(s). Line finder/final selector arrangements such as those disclosed in Specification 718,394 are employed, with the subscribers in 400-line groups. Each such group is associated with a switching arrangement involving a plurality of LF/FS units each unit comprising two primary switches PRI and one secondary switch SEC. A common control equipment CE (LF/FS), one of which is associated with each switching arrangement, connects a calling subscriber to an idle local transmission bridge equipment LTE over an originating trunk ORIG and is then released. LTE incorporates battery feed, and call metering and supervision arrangements for use on local calls, and also causes a register connector LRC to take an idle register REG into use. A loop dialling path is extended to the register, which reverts dialling tone and stores all the dialled digits. If translation is required, a common translator TRANS is taken into use. This contains a relay individual to each exchange code of the network, the operation of which signals to the register the routing digits, the call fee, and the number of numerical digits to be expected, after which the translator is released. The local transmission bridge equipments LTE are preferably arranged in groups of ten, each group being associated with a common control equipment CE (GS) at the group selector stage. The ten transmission bridge equipments have access to forty registers by using a 10 x 10 crossbar switch in the manner shown in Fig. 2. The ten trunks (LTE) are multipled on the bridges BR5-BR8 and by connecting the contact commons of these bridges to those of BR1-BR4 respectively, forty individual outlets which are terminated on registers are made available. A further bridge BR9 is used, as shown for the first and last commons at the foot of Fig. 2, for testing the forty registers ten at a time, by means of ten test relays HA-HK, by controlling four of the select magnets with respect to the bridge magnet. At the optimum time the register tests and takes into use the appropriate group selector common control equipment CE (GS) (Fig. 1). Ten 1000-line markers MKR (with relief markers if necessary) are provided for local calls, and the marker corresponding to the dialled thousands digit determines the location of the called line in a particular 400-line group and marks trunks TERM leading thereto, which are then tested by TS. The marker and CE (GS) are released as soon as LTE has been connected over PRI and SEC of the group selector to the selected trunk under control of switch CS. The transmission bridge equipment LTE then tests the wanted line and rings it and initiates metering, or reverts busy tone according as it is idle or busy, respectively. Outgoing calls.-The group selector common control equipment tests for an idle junction without using a marker. Junctions OA and OM, extending to automatic and manual exchanges respectively, have outgoing junction relay sets OTE1 and OTE2 specifically designed for the requirements and each incorporates a battery feeding bridge to which a through metallic path is presented by the local transmission bridge equipment. Metering is controlled by the junction relay set. Incoming calls.-Incoming junctions IA, IM, ITD from automatic exchanges, manual exchanges and test desks respectively, terminate on relay sets which incorporate battery feed equipment and can meet the signalling requirements of the remote exchanges. These sets are preferably arranged in groups of twelve, and an incoming register, connector IRC comprising a 12 x 10 crossbar switch can connect any set to one of ten registers. A junction relay set when taken into use indicates to the register the type of signalling which is to follow and whether the call is for a local termination, in which case the incoming digital signals will be numerical only. In this case the register signals to CE (GS) to seize a marker and the call is completed as for a local call. The trunking arrangements in the group selector are similar to those described in Specification 720,485. Detailed description.-Local transmission bridge equipment LTE (Figs. 5, 6). Part of the group selector primary switch PS is shown to illustrate the manner in which the transmission bridge equipments are terminated. The leads T, H, -, +, and OP in each of ten such bridge equipments extend to a single corresponding set of leads in the group selector common control equipment, and the ten conductors A1-T extend to the register connector LRC giving access to forty registers. The transmission bridge equipments are tested from a LF/FS for idle marking battery on the T wire over R4, and an idle equipment is seized by the calling loop, to which A pulls up. B follows and grounds lead RC to cause the seizure of an idle register which is held by the resistance loop including R7 presented to leads A1 and B1. The register returns resistance ground on lead SW, to which relay SW operates (JD staying down). The class of service of the calling line (viz. ordinary, coin-box, or route-barred) is indicated by a condition appearing at the incoming S lead which is extended over lead D to the register. The operation of SW extends lead OT to the outgoing P wire for use if the resulting call is an outgoing one, and diverts the calling loop to the register, which reverts dialling tone. Relay A is released, but B holds under control of SW, so that E operates and is followed by CA and MH. When sufficient digits have been received by the register, it tests the group selector common control equipment over lead T. If this is idle, ground applied to lead DD operates relay CC which grounds lead T of the register and lead H of CE (GS), and connects leads A2 and B2 of the register to leads - and + of CE (GS). Over this last path the register signals to CE (GS) whether the call is a local or an outgoing one, and, assuming the former to be the case, sends the number of the wanted party to CE (GS) by means of code'signals consisting of full and resistance ground. The register then releases, SW falls away, and A re-operates. When CE (GS), in association with a marker, has caused the wanted line to be marked, and a trunk to the appropriate 400-line group has been seized, the necessary switch magnets are operated in the group selector. The primary bridge magnet BM (PS) in the present case is operated by ground on lead OP and holds over contacts BM1 (PS), which release CC to disconnect CE (GS). Relay E falls away slowly. Contacts BM3 (PS) and BM2 (PS) disconnect tone lead NUT and the incoming T lead respectively. With SW down, H tests the wanted line over the P lead, and if it is free, pulls up, followed by J, which disconnects MH and the slow-to-release CA, and connects up ringing current; ring tone is reverted via relay A. If the wanted line were busy, MH would remain up and busy tone would be reverted as soon as E relapsed. On the reply of the called party, ring-trip relay F switches through, whereupon D pulls up, disables forced release relay FR, and brings up DD, which reverses the polarity on the incoming trunk. DD also places the operated bridge magnets under control of Hand FR, and re-operates E. J is thus disconnected and, during its release time, booster battery is connected to the caller's P wire to effect metering. Release.-If the called party clears first, the release of D connects up FR which operates after 30 seconds if the calling party has not cleared. FR then releases H and the bridge magnets in the group selector and terminating LF/FS, lights alarm lamp LPI, and operates a common alarm over lead CSH. If the calling party clears within the 30 seconds, the release of B disables the alarm arrangements. If the caller clears first, the relapse of H releases all the bridge magnets. Malicious call holding.-This facility is available on request for local calls, and is effected by plugging-up a subscriber's line to an interception relay set which applies a low resistance battery to the P wire. When a call is made to the line, this battery operates MH (Fig. 5) over its righthand winding, so that B is held independently of A and the release of the connection by the caller is prevented. MH also lights LP2 and operates an alarm over lead MCH, whereupon the calling party may be traced by an attendant. The facility may also be applied by a trunk operator who by a first momentary operation of her trunk offering key has heard the conversation. A second momentary oper